1. Field of the Invention
This invention relates to fastening means, especially for securing insulation material to metal roof deck. More particularly, the invention involves a plastic plate alone and in combination with threaded fasteners for assembling insulation to such roof deck prior to topping off the roof with plies of synthetic coating, tar, gravel or like materials.
2. Description of the Prior Art
Metal plates of various configurations are being used, with appropriate fasteners, to secure insulation material to metal roof deck. Some of the metal plates being used have a prefabricated central hole to accept the fastener, and generally because such plates are thin, they include a plurality of stiffening ribs. The plates include a substantial bearing surface to enable it to hold the insulation against the deck against wind loads.
Such metal plates are subject to various deficiencies. One problem with the plates is that due to the forces developed during any overdriven condition of the fastener, the metal tends to bend and curl and develop sharp edges from the permanent set. The sharp edges can then penetrate the plies of material disposed over the insulation, especially if persons walk on it. This penetration is undersirable since it breaks the moisture barrier introducing possible areas of leakage in the roof structure.
In addition, prior art metal plates have a central hole which offer no assistance in aligning the fastener, which penetrates the insulation and the metal roof deck. Any misalignment introduces the possibility of undesirable penetration or tearing of the insulation and is a potential source of roof leakage.
Moreover, to keep down the cost of the metal plates, they are made as thin as possible. Even where reinforcing or stiffening ribs are used, the area of the hole in the plate still remains weak and offers a potential problem since it is subject to being pulled over the fastener, particularly in high winds.
Another problem with metal plates is that they are often stored for periods of time at the job site or are exposed during installation and thusly must be galvanized or otherwise treated to prevent rust. Also, metal plates tend to collect moisture through condensation and the ribs define barriers which may collect water or solvents used with the upper ply.
Recently, a method of making a watertight joint in a sealing layer for a roof has been disclosed in U.S. Pat. No. 4,074,501. According to that patent, a sealing layer comprising a sheet of synthetic resin is secured to the external face of a roof with the aid of plates made of plastics or plastic-coated material and fastening means. However, this patent teaches the need for extra sealing, no anti-rotational means are disclosed, the insulation is caused to bend rather than be penetrated and it is directed to applications where the upper ply is under the fastener rather than over it.